1. Field of the Invention
This invention concerns the preparation of high load-carrying lithium soap greases having improved shear stability.
2. Description of Related Art
Various methods have been suggested for preparing lithium soap greases (see, for example, C. J. Boner, Manufacture and Application of Lubricating Greases, Reinhold Publishing Corp., New York (1954); NLGI Lubricating Grease Guide, Second Edition, Published by NLGI, Kansas City, Mo. (1987); as well as U.S. Pat. Nos. 2,898,296; 2,940,930; and 3,791,973; the disclosures of which are incorporated herein by reference). In all of these methods, conventional additives (e.g. anticorrosive agents, pour point depressants, dyes, and the like) are usually added to the grease in the final steps of its preparation to form a fully formulated grease.
More recently, copending patent application U.S. Ser. No. 080,454 filed Jul. 31, 1987, now U.S. Pat. No. 4,822,505, discloses that the load-carrying capability of greases containing a lubricating oil and a thickener can be significantly enhanced by incorporating therein a polyhydric alcohol having at least three hydroxy groups and at least two metal hydrocarbylthiophosphate compounds in which the metal is different in at least two compounds. The alcohol and the phosphate compounds are added to the grease during the final steps of its preparation.
However, none of these disclosures suggest that the shear stability of the high load-carrying lithium soap greases described in U.S. Pat. No. 4,822,505 can be improved by modifying the point at which the polyhydric alcohol is added during preparation of the grease.